The present invention relates broadly to telecommunications equipment. More particularly, the present invention is useful in the fiber-optic segment of the telecommunications industry as a device for selectively coupling a first optical fiber to a second optical fiber selected from a number of optical fibers, such as in an optical cross connect.
Over the past several decades, the telecommunications industry has exploded, and the incorporation of optical fiber into this industry is revolutionizing the way information is transmitted. Communication systems which use optical fiber as the transmission media offer some significant advantages over past wire-based systems, such as higher bandwidths and transmission rates, lower transmission losses, lower implementation costs, and greater electrical isolation.
Despite the benefits which exist in the optical transmission of information, one of the most difficult challenges in the widespread adoption of optical fiber in the telecommunications industry is the inability to route these optical signals effectively between optical fibers. The routing of these optical signals is typically accomplished using a cross-connect switch.
Historically, the switching of optical signals between optical fibers has included the detection and conversion of the optical signal to an electrical signal, and then switching and re-modulating the electrical signal to a new optical signal for transmission over a different optical fiber. Unfortunately, due to the power consumption and bandwidth limitations within the electronic switch circuitry and the expense of such a switching system, the optical-electrical-optical switch topology has not been widely adopted in the telecommunications industry.
Recently, a number of optical cross connect switches have been developed in order to switch optical signals directly from one fiber to another, thereby eliminating the need to convert the optical signal to an interim electrical signal. These optical switches incorporate various optical switch elements, such as mirrors, prisms, fiber collimators, and complicated drive mechanisms, to route optical signals through the switch. Unfortunately, some drive mechanisms are large, slow, and may severely limit the density of the switch. Also, due to the extremely tight tolerances necessary for proper angular alignment of the various reflective elements, and because the open-loop responses of these reflective elements is insufficient to step perfectly into position, a very sophisticated feedback control system is required, often resulting in these switches being prone to failure and requiring significant maintenance.
Despite the problems inherent to the optical switches currently available, single mode (SM) fiber, with its virtually unlimited bandwidth, has slowly become the standard in the telecommunication industry. Since the diameter of the core in a SM fiber is approximately ten (10) microns, the optical switches which use crude drive mechanisms are incapable of reliably switching the optical signals between fibers.
As the telecommunications industry continues to develop and grow to service more and more customers, the need for large scale, reliable optical switches will increase. Consequently, there is a need for an optical cross connect switch which can be readily integrated into existing telecommunications systems, and which can reliably switch optical signals from one of an array of SM input fibers, to one of an array of SM output fibers, and which can accomplish this switching quickly, with minimal power and at a minimal cost per channel.
The Optical Cross Connect Switch of the present invention includes three (3) basic components, including a beam generating portion, a beam directing portion, and a beam receiving portion. The beam generating portion receives a number of optical fibers which are each aligned with a lenslet for creating a communication beam. Another group of lenslets receive a light source, such as a light from a light emitting diode (LED), optical fiber, laser, vertical cavity surface emitting laser (VCSEL), and create a un-modulated companion alignment, or guidance, beam corresponding to each communication beam. The communication beam and its corresponding alignment beam are spatially separated, substantially collimated beams, and are aligned to propagate away from the beam generating portion to the beam directing portion.
The beam directing portion includes a first beam director and a second beam director, with each director having an array of beam-directing elements, such as micro electromechanical systems (MEMS) devices. Each communication beam and its corresponding alignment beam strikes a beam directing element on the first beam director, and is re-directed to a beam directing element on the second beam director, and propagates from beam directing portion towards beam receiving portion. The communication beam and its alignment beam may be substantially parallel, converging, or coaxial such that the two corresponding beams each strike the same beam director element.
The beam receiving portion includes a lenslet for each communication beam and a separate lenslet for its corresponding alignment beam. The lenslet focusses the communications beam onto an output fiber, and the separate lenslet focusses the alignment beam onto a position sensor. The focussed alignment beam creates a well defined xe2x80x9cspotxe2x80x9d whose position may be measured using classic spot centroiding algorithms, such as those techniques used in centroiding spots on a Hartmann sensor.
Importantly, the positional relationship between the communication beam and the alignment beam is known given any combination of beam directing elements in the first and second beam directors. Also, the positional relationship between the center of the output fiber and the sensor is also known. As a result of these known relationships, the position where the focussed alignment beam strikes the position sensor provides information regarding the position of the corresponding communication beam relative to the center of the output fiber. Thus, based on the position error feedback information from the position sensor, the beam directing elements are finely adjusted in order to precisely center the focussed communication beam onto the end of an optical output fiber, thereby increasing and potentially optimizing the amount of light received in the optical fiber. This method of precision alignment provides for an optical cross connect in which any input fiber may be optically connected to any output fiber, with minimal loss of the optical signal.